Merge PDF files in C# .NET

Merge multiple PDF files into one using C#

In the following code sample you can see how you can easily merge PDF files into one. It creates a new document and then adds a clone of the pages from each input document. Please take note that the input files will not be read until they are needed, so you can only close the input files until a copy has been made by writing the new document to the disk. This is done for efficiency: if you import a 1000-page document and only need the first page containing a certain keyword, then the rest of the pages will not be processed.

C# code sample: merge PDF

// Find all pdf documents in input folder.
DirectoryInfo directoryInfo = new DirectoryInfo(@"..\..\..\inputdocuments");
FileInfo[] allPDFs = directoryInfo.GetFiles("*.pdf");

// Create a document for the merged result.
Document mergedDocument = new Document();

// Keep a list of input streams to close when done.
List<FileStream> streams = new List<FileStream>();
foreach (FileInfo fileInfo in allPDFs)
{
    // Open input stream and add to list of streams.
    FileStream stream = new FileStream(fileInfo.FullName, FileMode.Open, FileAccess.Read);
    streams.Add(stream);

    // Open input document.
    Document document = new Document(stream);

    // Append all pages to target document.
    // The target document holds references to data in the input stream.
    // For efficiency it does not copy this data so the input streams
    // should not be closed before the merged document is saved.
    mergedDocument.Pages.AddRange(document.Pages.CloneToArray());
}

// Save merged document.
using (FileStream output = new FileStream(@"..\..\output.pdf", FileMode.Create, FileAccess.Write))
{
    mergedDocument.Write(output);
}

// Close all input streams.
streams.ForEach(stream => stream.Close());

VB.NET code sample: merge PDF

' Find all pdf documents in input folder.

Dim directoryInfo As New DirectoryInfo("..\..\inputdocuments")
Dim allPDFs As FileInfo() = directoryInfo.GetFiles("*.pdf")

' Create a document for the merged result.
Dim mergedDocument As New Document()

' Keep a list of input streams to close when done.
Dim streams As New List(Of FileStream)()
For Each fileInfo As FileInfo In allPDFs
    ' Open input stream and add to list of streams.
    Dim stream As New FileStream(fileInfo.FullName, FileMode.Open, FileAccess.Read)
    streams.Add(stream)

    ' Open input document.
    Dim document As New Document(stream)

    ' Append all pages to target document.
    ' The target document holds references to data in the input stream.
    ' For efficiency it does not copy this data so the input streams
    ' should not be closed before the merged document is saved.
    mergedDocument.Pages.AddRange(document.Pages.CloneToArray())
Next

' Save merged document.
Using output As New FileStream("..\..\output.pdf", FileMode.Create, FileAccess.Write)
    mergedDocument.Write(output)
End Using

' Close all input streams.
For Each stream As Stream In streams
    stream.Close()
Next